There's no right answer, it depends on what you want to find.
You can search for keywords on Heepsy. If you search for two or more keywords at the same time, Heepsy will show you profiles that use all those keywords.
For example, if you search "vegan desserts," you'll see profiles that mention animal-free sweets and treats. Or you could see some other use of the keywords, like "part-time vegan, loves desserts."
So if you want a more specific search, use multiple keywords. If you want to see broader results, search one keyword at a time.