I mostly travel solo nowadays, but have travelled with groups of different sizes in the past

Pros:

• you get to do whatever you want, whenever you want. No more endless debates about what to do, trying to please everyone and ending up pleasing none
• you can be more spontaneous and not need to plan in advance
• you can enjoy it more if you’re an introvert
• with modern phones it’s incredibly easy to not get lost

Cons:

• it can feel lonely at times
• you might need to spend more time on organizing the trip, compared to being in a group. But if you’re the one organizing the group anyway, you might actually spend less time when you’re solo. It really depends if you like doing this sort of thing
• it’s probably going to be more expensive, since you’re not splitting costs