I don't use the stuff.
If you've got your bicycle set up correctly, a good saddle, a good (not necessarily padded) pair of shorts, and if you wash (and dry) yourself during the ride you shouldn't need it.
EXCEPT: If the ride is exceptionally hot, and you are sweating up a storm, and washing yourself in convenience store washrooms or with baby wipes just isn't doing it ... you might consider a bit of cream. OR if the ride is exceptionally wet (pouring rain) you might consider a bit of cream. Wet skin is fragile skin and can benefit from a bit of added protection. I'll carry a small hand lotion with glycerine and/or silicone for that purpose.
I also carry Ozonol (similar to Polysporin) which has antibacterial properties and a painkiller. If it happens that I feel like I'm starting to develop some rawish areas, and washing myself with water or baby wipes isn't working anymore, I'll apply a very small dab of Ozonol. That one application usually takes care of the problem. Ozonol can also be used if you crash and you want to put something on the road rash.
If it happens that you finish your ride and you've got a bit of a rash (I get rashes because I'm mildly allergic to lycra ... yay!), shower, clean yourself very well, then apply a zinc oxide cream. Your rash will be gone by morning.