Stone pavers give you a defined, sharply-edged bed in your lawn. If you have plants spreading out of the bed, pavers can give them room without infringing
They also work well in yards with slopes, as they are adaptable to various angles. So, they're a good choice for gradual curves in the edging or a perfectly straight edge.
Most pavers are heavy enough that they won't slide around if installed correctly, but pavers with round edges that slide together, slightly interlocking, offer extra stability.