The Blues had a hit-and-miss window, with Antonio Conte missing out on some of his priority targets.
However, Chelsea splashed the cash, spending around £200m on Tiemoue Bakayoko, Danny Drinkwater, Alvaro Morata, Antonio Rudiger, Davide Zappacosta and Willy Caballero.
The Blues have had a fine start to the season under Conte, winning three of their opening four Premier League games, as well as cruising past Qarabag in the Champions League this week.
And Hazard says Chelsea spent well this summer, claiming the Blues can challenge for four trophies.
The Belgium winger told the Evening Standard: "It is important for Chelsea to have a strong bench because this season we have a lot of games.
"We are fighting for the Premier League, League Cup, FA Cup and Champions League, so we need to be ready for all of that.
"All of Chelsea's signings are internationals. You need quality when you play for this club because we want to win a lot of things.
"The more players we have the better it is for us. The bench was strong, it was good against Leicester.
"There was Willian, Batshuayi, me and so on - these kind of players can change the game. We all want to play and that's good.
"None of us want to sit on the bench, but we have a good team and the guys that started against Leicester deserved to play.
"We had a strong team last season, but we have a strong team this season."
