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, read the LP file, then optimize it, 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 in a manner that 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.