Vast majority of my trips are solo. You're totally free of doing whatever you want, eating where you want, changing plans at the last minute, easier to "go with the flow" and improvise. I like museums and cultural stuff too so I can take my time without thinking about the other person waiting for me, I like walking and kinf of getting lost in the city and I can do so without someone talking about how they tired or whatever. So yeah, it's cool. To travel with friends I guess it's better if the aim of the trip is the beach/party thing, but if it's to take some time off solo is cool.
Also anyway you can end up meeting people and whatnot, couple weeks ago I was in Madrid and used the coachsurfing app an went to a get-together with other travellers/locals, just to have a chat and chill out, so there's always that possibility too. I usually try to do some kind of tour (usually street art tour), that's also a good way to meet some people if one evening you want to grab some drinks with other people.