I guess it depends on individual circumstances. I have spare engines that fit several of my cars, so my two engine dollies make it easier to store them under the work bench, move them around in my shop and to and from the machine shop.
I have one heavy duty dolly that was given to me by a friend over thirty years ago that just has a slab of 2X12 wood bolted lengthwise into a welded angle iron frame with swivel casters at each corner. In addition to engines, it's perfect for moving transmissions, rear axles, front cross members, etc. I've even moved a bare chassis frame with it when I was doing a frame-off. When my garage was being built, it came in handy for receiving, moving around and storing the cast iron propane fueled wood stove until my contractor was ready for it to be installed in the office area. His crew were very happy not to have to manhandle it around like they usually do on other jobs. Then it was used for some of the components of my twin post shop lift until it was installed. When not in use, this essential piece of shop equipment it stands on end taking up very little space until it is needed again. My friend is long gone, but I thank him every time I use his home-made dolly.