We stayed at WL last year. We had a rental car and just didn't know when to use it, I guess. We thought the bus system would work. It works, but with small kids, it is not working well enough. For example, last year, with small kids, It took an hour to get back to WLfrom AK after waiting 20 min with wailing kids desperate for a nap. I also took 1 and 1/2 hours to get to Boardwalk area for dinner, partly my fault with a bad route plan.
This year, we did a bit better. We loved taking the boat to MK from WL. This works great. We could also take the boat to Contemporary and catch the monorail to get to TTC then Epcot which worked. But, we knew to drive the car to MGM and AK. Worked great. We also knew to drive to dinner at AKL. We also drove to Poly and GF for dinner, even though we could have done OK with the boat to the monorail. Driving decreases our frustration in the prolonged trips.
Another option. Cabs. Roughly $12. Last year we took one back to WL from the Boardwalk after our long trek to get there. This year, I took one from Epcot to Blizzard Beach with my 6 yo in the afternoon at 2 pm to go to that in the afternoon. This worked well. Also took one back to WL so we'd be on time for dinner. I wouldn't do it every time as it costs $, but it could save the day or evening with kids in a time or nap crunch.
So, having a car, and figuring out when you should use it versus WDW transport is an ongoing adventure.