Pianos come in two basic types — grands and uprights. Aside from looking different, there are many other differences in design and engineering that make these instruments function and perform quite differently.
Uprights were originally designed to save space and fit into a smaller room environment. The strings of an upright run vertically from the bottom to the top of the piano as contrasted to the horizontal stringing of a grand piano. Upright hammers strike the strings by moving forward laterally and return with springs. A grand design allows for the hammers to strike the strings from the bottom up to the string and utilizes gravity to return the hammer to a striking position. A grand piano mechanism repeats a note approximately 50% faster than an upright action.
The keys of a grand piano keyboard are considerably longer than those of an upright piano. The longer keys produce more leverage which allows for a faster and more responsive keystroke. Think of the difference between a seesaw with a longer board and one with a shorter board.
If all else is equal the grand piano will produce a larger range of tonal characteristics, repeat faster and play with more control to every musical nuance. The experience of playing a fine grand piano cannot be duplicated.
When budget or space is an issue, a nice quality upright piano can produce good results, but playing a fine grand is like stepping up to the next level.