The LP file format is designed to be human-readable. Gurobi writes coefficients in LP files with fewer decimal digits. Also, the LP file format does not necessarily preserve the ordering of variables. As a result, when you export a model to the LP format and read it again, the solution path may be different. Thus, the LP format is best used to visually inspect a model for correctness.
Gurobi writes MPS files with full precision and maintains variable order. Thus, the MPS format should be used when you want to ensure that Gurobi reads the exact same model that was exported.