Are ferry reservations recommended for foot passengers traveling late May/early June

We always prebook our ferry tickets for a few reasons:
We like to spread out our trip costs so purchasing in advance means not too large a CC bill when we return,
We know we have a seat and don’t have to give it another thought,
If you don’t have a ticket you have to go earlier to the pier and get in line to buy, tickets are not sold on the boats,
We are never disappointed that our ferry is fully booked.
Now, that said, we have traveled around the islands in September and early October, never have they been completely sold out. We haven’t travelled in May but my guess, and it is a guess, that no, you don’t have to pre purchase.
When we travel, i like peace of mind and prebooking gives me that.

Not sure if my answer will help you or not. We visited Croatia in September 2019, and it was quite busy at that time. Temperatures were in the 80's, and it felt like summer. Lots of tourists, lots of people still swimming. Restaurants were very busy.

We took the catamaran from Split to Hvar Town for a day trip. We were also foot passengers only; no car. We did not make reservations in advance. In fact, we purchased one-way tickets from Split to Hvar Town because we weren't sure what time we wanted to return to Split. We loved Hvar Town so much that we decided to take an early evening catamaran back to Split (instead of an earlier one), and we had no problems getting the tickets.

Hope this is okay to ask, Mark. Which ferry company did riders prefer, or are they all similar boats? I will be going from Split to Hvar - the town, and the next day from Hvar to Korcula - the town.

Krilo is the better ferry service.

Thank you, Barbara!

Hello Mark, here is a great article about the ferry from Split to Hvar It's mentioning all the ferry services and timetables/prices.