As others have stated, it's basically true that towers and comparable standmounts take up the same amount of space, but towers perform better on average. In the general case, it ends up being an aesthetics and portability choice. It's rare that portability matters and towers do look better IMO.
That said, the problem is that it's often not a general choice. There are many models with special features that only come in stand mount, for example Genelec Ones or the D&D 8C. Or the "tower" option is extremely expensive(W371A). If you want one of those models, as I did, you may end up stuck with stand mounts.
Particularly for multi-channel, there are also situations where a stand mount does fit better, for example if you want to put something underneath it for space reasons. In the system linked in my signature, the L/R surrounds sit above the side tables in my living room. Towers would not fit there. Additionally, if you are building a dedicated multi-channel system, having much larger L/Rs than the center is pointless, as the center bottlenecks overall output for nearly all multi-channel content.
But if both are in budget and the choice is between stereo generic 2-way passive bookshelf or generic 3-way passive tower... Buy the tower every time.