Adopt to the current booking trends used by the travelers the booking engine or your own reservation system is highly recommended
Now a days most of the travelers prefer to book their rooms and other travel services well ahead. So as a service provider you need to reach the travelers on time while they plan their trip.
Either your own reservation system or a feature rich booking engine to be integrated to your website in order to increase your online sales.
Save on commission paid to the travel agent for your customer, The customer comes to your site, since you don&t have reservation system integrated he/she will go to any of the OTA and book his room. For theses bookings you are paying commission unnecessarily to travel agent for your customer and also you are sending your customer to an open market place where in the customer might get diverted towards another hotel.