If you are doing an engineering course, in NAAC-A or B Grade University, per se, it doesn't matter in the long-term perspective. However, on the short-term it does. The precise clarity is as follows:

NAAC grade doesn't get endorsed in your certificate so it doesn't impact your further career. No one in the industry shall ever ask you whether you belonged to an Alma mater with A or B NAAC grade.

Where it matters is that if you are studying in NAAC A, A+ or A++ Grade university, it is almost given that the institute does hold superior credentials and delivers high on academics as well as preparing students for the future. Industries do also recognize these top graded universities better than B grade universities and hence students placements become much easier. It also gives an instant confidence in students that the level of peers in the classroom, teachers, project support and infrastructure would be decidedly better than the NAAC B grade universities. In nutshell, it surely augurs well to be studying in the university that is awarded NAAC accreditation in "A" series.