App installing takes a long time in a Work Profile
There won't be any real damage when you  turn off MIUI optimisation.

This post describes the effects of having MIUI optimisation turned on/off as reported by MIUIers.

The optimisation offers some MIUI based settings &amp; optimizations set by developers with aim of giving a fast user experience but of late has offered more disadvantages especially in new ROMs. 

It has been reported to cause some some incompatibility issues with Google based apps and sync services and also non functionality of Greenify hibernate feature in non-root mode (MIUI 9.xx) althought it doesn't affect MIUI 8.

Therefore, you can safely turn it off, if it is causing lag issues With work Profile, as much as it is recommended to be off when using Greenify (MIUI 9). Besides the changes described in the linked post (as a MIUI user) I don't see any detrimental effects when you disable it.