It depends. If you take summer classes so you can finish a degree in 4 years while only taking 12 credits a semester, that's not good unless you have a good reason such as full-time employment. If you take summer courses at an "easier" school it won't be as favorable as taking them at a harder school but it's definitely not a deal-breaker, especially if your reasons for doing it included things like saving $ or leaving time to pursue a major in a different field at your home school. Taking summer classes at your home school is completely fine, especially if you are also taking a full load during the academic year.