Remember, an old computer will be limited to it's speed spectrum. If a game demands a faster system, or is speed sensitive, it can be troublesome to get the smooth gameplay.

If the game is speed sensitive and was programmed for slower systems, it will be too fast to run them on new systems.

If it is a demanding game, then if the pre-built system can't keep up, you need to upgrade the system.
Or you need to maintain multiple machines to play particular games on them to run them as they were intended to.

Dosbox takes care all of these and you can tune Dosbox cycles to match the exact smooth gameplay you want. So, you can play a game designed for XT or 486 comfortably in Dosbox. Most of us nowadays would already be running fairly contemporary CPUs in our main desktops or laptops, and this wouldn't be a problem of using Dosbox for playing these demanding games.

As I have recently posted in the Dosbox General forum, you can even play DOS SVGA flight sims comfortably and smoothly in Dosbox using current gen CPUs.

It all falls down to either you want to maintain multiple systems (and the accompanying space hog, multiple wires and power connections and peripherals for EACH system), to play a wide range of DOS games, or use Dosbox for playing.

As a hobby of keeping vintage systems, Dosbox can't be pulled in and compared to real machines, because the purpose of Dosbox is solely for playing DOS games in modern machines without hassle. For those who like to keep many machines as collections, it's a different matter. You can't equate Dosbox there because the purpose is different - collecting hobby.

This is coming from me who currently have a 486DX2-66, a Socket 5 Pentium 133 Voodoo 1, a Slot-1 Pentium II 400 unlocked CPU Voodoo2 SLI system and a P4 3.6GHz based Win9x/W2k system. And I'm not using all these much anymore because, maybe I have already built my favourite systems, but most importantly, Dosbox with MUNT, Yamaha XG software synthesizer and Sound Canvas plugin takes care of all my needs in my core i7 based main desktop and laptop, and even in my core M tablet. The convenience of emulating the MT-32 using MUNT is a godsend. Without the wires, speakers and extra power adapters, and there's no need to get stuck in a room with a ISA and a MPU-401 intelligent mode compatible ISA card to connect to the MT-32. (Yes, I still have the MT-32 and SC-55). Some say, it's not as good as the real thing. But for me, these have taken a long stride, and I can't tell the difference.

As most have mentioned, with Dosbox, you are able to eliminate one of the perennial annoyance - memory management.

And for me, convenience takes the precedence. Now I can play a SIerra game using Dosbox, complete with MT-32 sounds using MUNT, or DOOM with Yamaha XG synthesizer or Warcraft with Sound Canvas plugin, wherever I am, using my Dell Windows 10 tablet. And I don't need to get tied down in a room with big machines with ISA slots with 100% MPU-401 ISA card (which I also have) connected to modules to listen to all these.

For purists' argument sake, I have both - machines, which I'm no longer using that much, and Dosbox - which I prefer, mainly for convenience. (I'm a collector too, but not as aggressive as I was before).

(And I also use 86Box for my Windows 95-based tinkering and games. Also for playing around with various classic machines, complete with BIOS and experimenting with various DOS / OS/2, etc.)

Actually MUNT made me sell off 2 of my Roland CM-500s and even 2 of my LAPC-Is. 😉