From the below linked story:
"Operating her own server would have afforded Clinton additional legal opportunities to block government or private subpoenas in criminal, administrative or civil cases because her lawyers could object in court before being forced to turn over any emails. And since the Secret Service was guarding Clinton's home, an email server there would have been well protected from theft or a physical hacking."
AP News: Clinton Ran Own Computer System for Her Official E-mails
"Operating her own server would have afforded Clinton additional legal opportunities to block government or private subpoenas in criminal, administrative or civil cases because her lawyers could object in court before being forced to turn over any emails. And since the Secret Service was guarding Clinton's home, an email server there would have been well protected from theft or a physical hacking."
AP News: Clinton Ran Own Computer System for Her Official E-mails