Yes, they can.

But now ask this question -

Can sculpties improve lag?

Yes, they can.

Oh my. How do we get the same answer to the opposite question?

The answer lies with how you use sculpties. Design is everything.

The two culprits to why sculpties cause lag and can improve lag are the two Ts:

Textures and triangle count

Textures

Sculpties require two textures - one for the sculpt map and one for the color texture. That’s a serious improvement over some varieties of the famous cut and twisted torus, which actually can and do outclass sculpties for lag. Each cut side of a tortured twisted hollowed torus (or its friends - the ring and the tube) requires a texture - if its a realistically textured torus, you could be looking at double or more of the textures a sculptie uses.  Cut and twisted tori still outrank sculpties in sheer triangle count - part of what lead to the development of the sculptie was to minimise use of these prims in attachments such as hair and shoes. Hair made from sculpties are far more efficient in terms of client lag than their torus created kin. They use less prims - which translates to fewer textures and to our next topic of discussion - triangle count.

Triangle count

There is nothing more lagariffic than entering a sim with sculpties that comprise every bit of plant life and landscaping. In many cases, sculpties are modelled very inefficiently, resulting in far more used than necessary, causing a huge download for the visitor, who may not ever see your build download entirely. Even with repeating textures on every sculpt, the client lags horrifically on some lower end systems. Why? Triangle count is your culprit. This is the single most taxing thing your computer graphics card has to do, render everything around you. Simply put, more triangles in your scene means more for your graphics card to display to you. It’s why even the next generation games resort to tricks to fool the eye into believing there are more polygons than actually are there - with technology such as normal and parallax mapping.

So you want to do two things - reduce your textures and triangle count, therefore reducing client side lag for your visitors. Reducing textures also reduces sim lag - the single most frequent reason for sim reboots in my experience, is for image cache times skyrocketing.

Rules of thumb with sculpties and textures.

Use as small textures as possible for your sculpt maps and color textures.

Sculpt maps do not need to be larger than 128 x 128 pixels, and can be as small as 64×64 pixels. For landscaping sculpts - consider whether you really need to use lossless uploading - there is usually not much difference in appearance for terrain and rock sculpties and the load times for lossy sculpts are dramatically faster.

Use texture atlasing and offsets - a large texture comprising many small textures can dramatically decrease loading time for color textures. Many times you don’t need larger than a 256 x 256 texture for landscaping sculpties (sometimes even 128×128 will do you!), and you can fit four of those 256×256 textures on one 512 texture. Oftentimes repeating textures work just fine for landscape sculpties too. Another method is to build a large one piece multipart sculptie which you then cut apart in a uvmapping application to create smaller sculpties (use UVMapper for this!) - while creating a full color texture across the uncut sculpt to use as an instant texture atlas.

And the one time I will break the rule on 1024×1024 - if you find you can put ALL your color textures in your build on one or two 1024 textures - do it. Your textures will load far faster for your visitors, and as a result, your sculpties will be faster to load too. Fewer calls to the asset servers is why this works.

Rules of thumb with sculpties and triangle count.

Be an efficient sculptor. Think of how you can use one sculpt to comprise what several prims might have ordinarily done.

For large landscape areas - use megaprims when the situation calls for it. Why megaprims? Because you can dramatically reduce the amount of sculpt prims, and therefore sheer triangle count. (as a side effect, fewer sculpt textures as well!) The beauty of megaprims and sculpties means you can develop landscapes that look more aesthetically pleasing in both shape and color, yet reducing the number of prims that you’d have ordinarily used. Keep them phantom and build normal transparent collision prims for people to walk on - they’ll never know the difference. As the collision prims are invisible, you can model them more efficiently without trying to make them look pretty (which is effectively impossible for organic structures) - stick to the box and cylinder prims (and the occasional sphere, if necessary) for this.

For many sculpted terrain areas - you can even use the sim terrain itself as the collision plane, terraformed to lie just underneath the sculpted phantomed prim. You can achieve interesting terrain effects this way, by clever use of sim terrain textures combined with sim terrain terraforming and sculpted terrain.

And lastly - don’t use sculpties when a regular prim would have been equally fine with a good texture map. Boxes and cylinders still have far fewer vertices than a sculptie does, use them when the situation calls for it, especially in background and fill areas where fine detail isn’t necessary. Sculpties are best for those large organic models that would have been high prim and not nearly as aesthetic to do the old fashioned way. Yes, this means that you can make small filler vegetation just fine with two box prims and a good texture. Use billboarding when the situation calls for it!

I hope this missive helps a few folks!