Generally, it depends on the situation whether you use IP or not. The factors are your company size, available manpower, cost, time to market and so on.
For example, your company would like to make a new IC chip. There is an idea, block design. You calculate the cost and time to market with your available manpower. One of the blocks needed in your chip is PLL. Your company has never designed any PLL or designed but not with such parameters (more hard to achieve) as required in your chip. Hence, you do calculation what would be the time-cost to design it by yourself and do a research on the market (contact with PLL IP providers). It may happen that it is less risky or even cheaper to use IP.
Really, it depends a lot on many factors whether IPs are used. Generally, they are used a lot as you get silicon proved IP almost immediately from such companies as Synopsys, Cadence and so on. Moreover, a lot of design companies which specialize in particular areas (e.g. power management, NFC, PLL, ADCs) are used by other companies to help them during projects in terms of design services (not IP but design services).